The present invention relates to a method and a configuration for the generation of a vehicle reference speed as a reference value for the control of brake slip and/or traction slip in automotive vehicles wherein the rotational behavior of the controlled wheels is measured, and the vehicle reference speed is defined by virtue of the rotational behavior of the individual wheels by way of logic combining, selection according to predetermined criteria and/or comparison with predetermined limit values.
In brake slip or traction slip control systems, precise vehicle reference speed as a reference value for the control action is the precondition for obtaining high quality of control. As the measurement of the actual vehicle speed with the aid of direct measuring methods such as radar or by means of a freely running wheel entails relatively great effort and involves additional disadvantages, it is preferred to derive the vehicle speed from the rotational behavior of the controlled wheels, which has to be determined anyway, by logic combining of the signals and by judicious selection, and by defining a vehicle reference speed appropriate for the control.
As long as the wheels encounter no brake slip or traction slip or only a low value thereof, the formation of the vehicle reference speed is relatively easy. However, when slip increases at one or at several of the wheels, this has to be taken into account when defining the reference value. There are two problems: on the one hand, control actions are required to be taken to gain the optimum information from the individual behavior of each separate wheel, while, on the other hand, those signals have to be detected from the combination of all wheels participating in the reference formation which represent the vehicle reference speed most precisely or which are best suited for the formation of the vehicle reference.
Methods are known for the purpose of anti-skid control wherein the reference value serving as the vehicle reference speed follows in principle the speed of the respectively fastest, second-fastest or third-fastest controlled wheel, while decreasing, however, at most with a gradient (-1 g) corresponding to the acceleration, which gradient is derived from the theoretic maximum of deacceleration (German printed and published patent application No. 22 54 295).
Moreover, anti-skid control systems are known wherein the negative gradient of the vehicle reference speed, depending on the road condition, takes on various predetermined values for better approximation to the actual vehicle speed variation (German printed and published patent application No. 22 09 955). Other anti-skid control systems of this type are arranged to determine the discrepancy of the wheel speed signals from the reference signal in terms of magnitude and/or direction at the end of the control cycle, and are arranged to change the negative gradient of the reference value as a function of the determination for the purpose of adapting to the vehicle speed variation (German printed and published patent application No. 28 36 778).
All known methods for the formation of the vehicle reference speed bear the disadvantage that under circumstances such as very low value of friction (icy roads, slippery roads) or with rapidly changing road conditions, the vehicles reference deviates excessively from the vehicle speed and is thereby inappropriate as a reference value for slip control.
It is therefore the object of the present invention to provide a method for the generation of a vehicle reference speed which permits deviation of optimum information from the individual rotational behavior of the wheels, the information enables the derivation a suitable vehicle reference speed by way of combination and selection.